SSRS Dynamic percentage column value

Hi. I have an SSRS report. Within a Tablix how do I create a percentage column that works out the result based on two other values with the table?

See below:

In the % Total Demand column how do I for each row dynamically work out the total / the value * 100

e.g. For the first row whats the % Demand for Portfolio 5.5+5.5+0.3 / 5.5 * 100 (or something along those lines)

Looking at this I guess the % Total Demand row should sit horizontally.

Thanks!